1. Field of the Invention
This invention relates to an information signal reproducing apparatus adapted for reproduction of information signals from recording tracks formed on a record bearing medium.
2. Description of the Prior Art
Reproduction of video signals from, for example, a record bearing medium having a plurality of information recording tracks formed thereon in concentric circles, requires a reproducing head to be under tracking control, the precision of which must be increased, accordingly, as the adjoining tracks are more closely spaced for increased recording density.
However, the record bearing medium expands or contracts according to changes in the ambient conditions, such as temperature and humidity. Besides, the positions of the recording tracks vary with differences between the recording apparatuses used.
Therefore, even in cases where a reproducing apparatus for reproducing information signals from such recording tracks is arranged to have a reproducing head positioned at a predetermined point, there inevitably arises some positional discrepancy between the reproducing head and the track. This discrepancy has prevented production of recorded signals in a satisfactory manner. To solve this problem, it has been proposed to perform tracking control by adjusting the position of a reproducing head on the basis of the reproduction output of the reproducing head. In one example of such prior art methods, the reproducing head is minutely vibrated and coincidence- between the vibration frequency and the fluctuating frequency of the reproduction output is arranged to be detected. However, this method necessitates an extremely complex structural arrangement.
Meanwhile, there has been contrived a system, wherein, in cases where different information signals are to be recorded in different tracks, these tracks are numbered and a reproducing apparatus is arranged to designate an applicable track number in obtaining a desired information signal.
However, in the event of a low reproduction output level of the reproducing head or in the event of absence of any signal in the designated record track, reproduction tracking under the above-stated shifting control would cause the reproducing head to be excessively shifted over to another track located adjacent to the applicable one. In that event, the track numbers get out of control. A reproduced track then differs from a designated track. Once such a discrepancy arises, it is no longer possible to designate a reproducing track number from outside unless a track number is written in each of the record tracks.